Navigation Links
Hearing the telltale sounds of dangerous chemicals
Date:8/14/2012

WASHINGTON, Aug. 14, 2012-- To warn of chemical attacks and help save lives, it's vital to quickly determine if even trace levels of potentially deadly chemicalssuch as the nerve gas sarin and other odorless, colorless agentsare present. U.S. Army researchers have developed a new chemical sensor that can simultaneously identify a potentially limitless numbers of agents, in real time. A paper describing the system has been published today in the Optical Society's (OSA) journal, Optics Letters.

The new system is based on a phenomenon known as the photoacoustic effect, which was discovered by Alexander Graham Bell, in which the absorption of light by materials generates characteristic acoustic waves. By using a laser and very sensitive microphones -- in a technique called laser photoacoustic spectroscopy (LPAS) -- vanishingly low concentrations of gases, at parts per billion or even parts per trillion levels, can be detected. The drawback of traditional LPAS systems, however, is that they can identify only one chemical at a time.

"Photoacoustics is an excellent analytic tool, but is somewhat limited in the sense that one traditionally only measures one absorption parameter at a time," says Kristan Gurton, an experimental physicist at the U.S. Army Research Laboratory (ARL) in Adelphi, Md. "As I started looking into the chemical/biological detection problem, it became apparent that multiple LPAS absorption measurements -- representing an 'absorption spectrum' -- might provide the added information required in any detection and identification scheme."

To create such a multi-wavelength LPAS system, Gurton, along with co-authors Melvin Felton and Richard Tober of the ARL, designed a sensor known as a photoacoustic cell. This hollow, cylindrical device holds the gas being sampled and contains microphones that can listen for the characteristic signal when light is applied to the sample.

In this experiment, the researchers used a specialized cell that allows different gases to flow through the device for testing. As the vapor of five nerve agent mimics was flowed in, three laser beams, each modulated at a different frequency in the acoustic range, were propagated through the cell.

"A portion of the laser power is absorbed, usually via molecular transitions, and this absorption results in localized heating of the gas," Gurton explains. Molecular transitions occur when the electrons in a molecule are excited from one energy level to a higher energy level. "Since gas dissipates thermal energy fairly quickly, the modulated laser results in a rapid heat/cooling cycle that produces a faint acoustic wave," which is picked up by the microphone. Each laser in the system will produce a single tone, so, for example, six laser sources have six possible tones. "Different agents will affect the relative 'loudness' of each tone," he says, "so for one gas, some tones will be louder than others, and it is these differences that allow for species identification."

The signals produced by each laser were separated using multiple "lock-in" amplifiers -- which can extract signals from noisy environments -- each tuned for a specific laser frequency. Then, by comparing the results to a database of absorption information for a range of chemical species, the system identified each of the five gases.

Because it is optically based, the method allows for instant identification of agents, as long as the signal-to-noise ratio, which depends on both laser power and the concentration of the compound being measured, is sufficiently high, and the material in question is in the database.

Before a device based on the technique could be used in the field, Gurton says, a quantum cascade (QC) laser array with at least six "well-chosen" mid-infrared (MidIR) laser wavelengths would need to be available.

"There are groups of researchers producing QC laser arrays that will operate with sufficient power, and will house as many as 10 -- or more -- lasers at different frequencies in the spectroscopically rich region of the MidIR," he says.

Once such laser arrays are available, the method ultimately "could be tailored for a variety of detection scenarios ranging from the obvious need to protect our soldiers during conflict to civilian applications like detecting the presence of harmful chemical gases that are difficult to detect with conventional techniques," Gurton says. A sufficiently rugged device for in-the-field use, he envisions, could be about the size of a milk carton. "A photoacoustic cell is surprisingly simple and inexpensive to produce, with all of the cost and size driven primarily by the packaging of the quantum cascade laser array," he adds.

In theory, the method could be used to identify an unlimited number of chemical agents.

"In our paper we demonstrated the ability to measure as many identifying absorption features as you want," Gurton says. "You're only limited by the number of laser sources available." However, he notes, "at some point, as the number of species spectra increase in the database, a degree of spectral overlap would occur, which might result in erroneous identification. It just depends on how similar the spectra are to each other. You could have just two that have very similar spectra and that could cause problems, or you could have 20 to 30 species spectra that all have distinguishable features that can be identified easily."


'/>"/>

Contact: Angela Stark
astark@osa.org
202-416-1443
Optical Society of America
Source:Eurekalert  

Related biology news :

1. Cichlid fish: How does the swim bladder affect hearing?
2. Study of zebra fish mouth formation may speak to Fraser syndrome hearing loss
3. Can you hear me now? New strategy discovered to prevent hearing loss
4. Stem cell transplantation into mouse cochlea may impact future hearing loss therapies
5. Gene therapy for hearing loss: Potential and limitations
6. Study amplifies understanding of hearing in baleen whales
7. Manatee hearing good enough to sense approaching motorboats
8. Specialization for underwater hearing by the tympanic middle ear of the turtle
9. Teaching about hearing can save young peoples ears
10. Mystery of elephant infrasounds revealed
11. What sounds good doesnt always taste good
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Hearing the telltale sounds of dangerous chemicals
(Date:5/16/2017)... N.J. , May 16, 2017  Veratad Technologies, ... provider of online age and identity verification solutions, announced ... K(NO)W Identity Conference 2017, May 15 thru May 17, ... Regan Building and International Trade Center. ... the globe and in today,s quickly evolving digital world, ...
(Date:5/6/2017)... , May 5, 2017 RAM ... announced a new breakthrough in biometric authentication based ... quantum mechanical properties to perform biometric authentication. These new ... semiconductor material created by Ram Group and its ... entertainment, transportation, supply chains and security. Ram Group ...
(Date:4/19/2017)... York , April 19, 2017 ... as its vendor landscape is marked by the presence ... market is however held by five major players - ... Together these companies accounted for nearly 61% of the ... the leading companies in the global military biometrics market ...
Breaking Biology News(10 mins):
(Date:10/7/2017)... ... October 06, 2017 , ... Phase ... metagenome deconvolution product, featuring the first commercially available Hi-C kit. Researchers can ... Hi-C metagenome deconvolution using their own facilities, supplementing the company’s full-service ProxiMeta ...
(Date:10/6/2017)... ... October 06, 2017 , ... The HealthTech Venture Network (HTVN) ... their fourth annual Conference where founders, investors, innovative practitioners and collaborators are invited ... competition showcasing early stage digital health and med tech companies. , This day-long ...
(Date:10/5/2017)... ... October 05, 2017 , ... LabRoots , the leading ... around the world, is giving back to cancer research with a month-long promotion supporting ... Now through October 31, shoppers can use promo code PinkRibbon to get 10 percent ...
(Date:10/5/2017)... Baltimore, MD (PRWEB) , ... October 05, 2017 ... ... over $1.7M to develop new applications of its Nanobind DNA/RNA extraction technology ... micro- and nanostructured silica on the surface and that can be used for ...
Breaking Biology Technology: